The present invention relates generally to determining the peroxide content of materials which may contain peroxide, more specifically, to a method and apparatus for determining the peroxide content of hydrocarbon fuels, such as, jet fuels and diesel fuels.
Hydrocarbon fuels, such as jet fuel, gasoline, diesel fuel and kerosene, are typically stored for a period of time before use. During transportation, bulk storage or storage in engine tanks or other containers, hydrocarbon fuels are frequently subject to the oxidative formation of peroxide compounds in the fuel, in particular, the formation of hydroperoxides. The presence of these peroxides accelerates both the formation of gums, sediments, and other insoluble substances in the stored fuels and the degradation of engine components. Thus, stored and transported hydrocarbon fuels need to be monitored for peroxide formation.
Peroxide in fuels degrades to aldehydes. The thermal input typically experienced by fuels further causes aldehydes to produce carboxylic acids and phenols. The use of a fuel can result in excessive component wear and eventual equipment failure. It is undesirable to use fuels beyond their useful life. However, as a conservative precautionary measure, fuels left in storage may require premature re-refining, reprocessing or disposal. This approach, consequently, results in the premature discard of fuel with useful lives. Early detection of content is important in monitoring the continued viability of fuel. Early detection would allow more efficient use of these materials thereby saving in material, labor and equipment costs.
Peroxide content can be measured with commercially available peroxide teststrips, such as for example, MERCKOQUANT 10011 PEROXIDE TEST, from EM Science of Gibbstown, N.J. However, peroxide test strips are not acceptable to hydrocarbon fuel users since the test strips produce an approximate range of peroxide content, are based on hydrogen peroxide not organic hydroperoxides present in stored fuels, and require a volatile, peroxide-free ether for dilution purposes prior to testing.
The only test formerly acceptable for performing peroxide evaluations of jet fuels is ASTM Method D3703-85 titled "Standard Test Method for Peroxide Number of Aviation Turbine Fuels". The ASTM method is a titration method in which a quantity of fuel is dissolved in an chlorinated solvent and mixed with potassium iodide. The potassium iodide reduces the peroxides present in the fuel. An equivalent amount of iodine is then liberated. The peroxide level in the fuel is then determined by titration of the liberated iodine with sodium thiosulfate solution.
The ASTM method has a number of distinct drawbacks which make routine and remote peroxide measurement impractical. It is time consuming, tedious and expensive. First, as the ASTM method requires a titration, remote on site analysis is very impractical due to the fragility of the equipment, chemicals required and expertise of personnel required to conduct the titration. Further, the ASTM method generates up to 460 milliliters of chlorinated waste per sample tested. Due to environmental considerations, the use of chlorinated solvents is quite costly due to special waste disposal methods required for chlorinated waste. Multiple testing of a sample is impossible as each titration requires a fresh solution. Finally, 11 minutes of time are required per sample analyzed. Thus, for triplicate analysis of a supply of fuel over 30 minutes in a laboratory would be required.
U.S. Pat. Nos. 4,744,870 and 5,071,527 to co-inventor Kauffman disclose the voltammetric analysis of antioxidant containing oils and lubricants. A sample is mixed with a solvent, an electrolyte and an organic base. A potential is then swept across the sample while measuring the current. However, neither the '870 patent or the '527 patent measure peroxide level nor do they add an aqueous solution of potassium iodide. Rather, they both measure the amount of remaining antioxidant in the oil or lubricant to determine the remaining useful life of the oil or lubricant.
U.S. Pat. Nos. 4,764,258 and 5,239,258 also to Kauffman relate to voltammetric methods for evaluating lubricating oils in the former and fuels, food and oils in the latter. A sample is mixed with a solvent, an electrolyte and then subject to sweeping potential while the current is measured. However, in U.S. Pat. No. 4,764,258, an antioxidant additive is analyzed for while in the U.S. Pat. No. 5,239,258 the degradation products analyzed are aldehydes and phenols. Peroxides are not analyzed in either patent. Both patents also do not add an aqueous solution of iodide and, thus, cannot determine peroxide levels in a sample.
Accordingly, there remains a need for quick, accurate determination of peroxides in hydrocarbon fuels which may contain peroxide including jet fuel, diesel fuel and gasoline.